Electrodeposition of Pt nanoclusters on the surface modified by monolayer poly(amidoamine) dendrimer film

Preparation of Pt nanoclusters on the poly(amidoamine) (PAMAM) modified surface by electrodeposition was firstly reported. The presence of PAMAM could affect the growth of Pt nanostructures. Field-emitted scanning microscopy images showed that these nanoclusters were not common nanoparticles but were consisted of many small nanoparticles. The size of them could be controlled and the deposition mechanism was also discussed. This method would give a route of preparing novel nanostructures by electrodeposition.     

Layer-by-layer assembled thin films composed of carboxyl-terminated poly(amidoamine) dendrimer as a pH-sensitive nano-device

Dendrimer-containing multilayer thin films have successfully been prepared by a layer-by-layer deposition of carboxyl-terminated poly(amidoamine) dendrimer (PAMAM–COOH) and poly(methacrylic acid) (PMA) on a solid surface at pH 4.0, while the multilayer film did not form at pH 7.0. The PMA/PAMAM–COOH multilayer films prepared at pH 4.0 are decomposed at neutral pH due to electrostatic repulsion between negatively-charged carboxylate residues. The results suggest that the primary force for the successful deposition of PAMAM–COOH and PMA at pH 4.0 is hydrogen bonding between COOH residues on the surface of the dendrimer and PMA. The multilayer films are decomposed also at strongly acidic pH, suggesting an electrostatic force of attraction between the protonated tertiary amino groups in PAMAM–COOH and a small fraction of COO⁻ residues in PMA contributes in part to the multilayer formation at pH 4.0. The PMA/PAMAM–COOH thin films can accommodate model dyes, Rose Bengal and 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonate, and the release can be controlled by changing pH.     

Decomposition of poly(amidoamine) (PAMAM) dendrimers under O2 plasma conditions

Results of FTIR and XPS measurements of bulk and γ-Al₂O₃-supported fourth generation hydroxyl-terminated (G4OH) poly(amidoamine) (PAMAM) dendrimers during O₂ plasma treatment at room temperature indicate that such treatment can effectively decompose the structure of the dendrimer. No new functionalities appear in the dendrimer structure during such treatment, but instead fragmentation of this structure is taking place. The dendrimer backbone likely disintegrates into small molecules (i.e., NO_x, CO, CO₂) which in the case of the supported dendrimers interact with the γ-Al₂O₃ support and form surface nitrate and carboxy species. Subsequent treatment in H₂ at 300 °C leads to the complete removal of the nitrogen-containing species from the surface of γ-Al₂O₃. However, carbon-containing species still remain on the surface in relatively small amounts. Finally, XRD measurements further show that the crystallinity of the support is not affected substantially by the O₂ plasma treatment.     

PAMAM (poly-amido amine) dendrimer supported copper nanoparticles for chemoselective nitro reduction

Present paper reports the synthesis of biocompatible poly (amidoamine) (PAMAM) dendrimer by Michael addition (up to Generation 2) which has been used as a matrix for preparing copper nanoparticles using green solvent. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy – dispersive X-ray spectroscopy (EDX) were used to determine the surface morphology and elemental composition of the nanoparticle. The results confirmed the FCC structure of the prepared dendrimer encapsulated Cu nanoparticles with an average crystallite size of 4 ​nm. Purely aqueous-phase chemoselective reduction of nitro group in various aromatic nitro substrates such as p-nitrophenol, p-nitrobenzaldehyde and 2, 4 dinitrophenol have been employed in the presence of eco-friendly dendrimer encapsulated Cu nanoparticles using hydrazine hydrate as reducing agent. The nanocatalyst showed high reusability up to seven runs exhibiting no significant loss in its catalytic activity. As the synthesised material is found to be biocompatible, this catalytic strategy can be used to catalyse similar biochemical reactions.     

9-Anthracenecarboxaldehyde Functionalized Second Generation Poly（amidoamine） Dendrimers： Synthesis and Metal Absorption

Dendrimer nanocomposites (DNCs) are organic/inorganic hybrid materials, composed of nanosized particles, which display unique physical and chemical properties due to the dispersion interactions between the inorganic guest and the organic macromoleculars h…     

Structural deviations in poly(amidoamine) dendrimers: a MALDI-TOF MS analysis

A step-by-step synthesis/purification (CC, HILIC, HPLC) of poly(amidoamine) PAMAM dendrimers was performed. MALDI-TOF MS in the linear and reflectron mode was used to analyze the purified samples and byproduct samples of G0-G5 generations of the dendrimers up to the mass of 35 000 Da. DHB/fucose was found to give the best resolution, causing the least fragmentation of the samples. The precise mass number for the ideally branched dendrimers and their “structural errors” was obtained. The profile of the structural errors was established.     

Synthesis and characterization of tri(ethylene oxide)-attached poly(amidoamine) dendrimer layers on gold

This paper describes the synthesis of a tri(ethylene oxide)-attached fourth-generation poly(amidoamine) dendrimer (EO3-dendrimer) and the characterization of its layers on gold. NMR analysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that about 61 amine groups of a G4 PAMAM dendrimer were covalently conjugated with tri(ethylene oxide) units, accounting for a 95% modification level. Layers of the EO3-dendrimer were formed on gold, and the resulting surface was characterized by infrared reflection absorption spectroscopy, ellipsometry, and contact angle goniometry. The EO3-dendrimer resulted in more hydrophilic and less compact layers with no substantial deformation of the molecule during layer formation by virtue of the EO3 units, compared to a PAMAM dendrimer. Interestingly, the specific binding of avidin to the biotinylated layers of the EO3-dendrimer approached a surface density of 5.2 +/- 0.2 ngmm-2, showing about 92% of full surface coverage. The layers of the EO3-dendrimer were found to be more resistant to nonspecific adsorption of proteins than PAMAM dendrimer layers when bovine serum albumin and serum proteins were tested.     

Cinnamoyl shell‐modified poly(amidoamine) dendrimers

Poly(amidoamine)(PAMAM) dendrimers with a cinnamoyl shell were prepared by reacting full generation PAMAM dendrimers (G=3.0) with 2‐chloroethanol and cinnamoyl chloride, which resulted in densely packed polymerizable unsaturated groups on the periphery. The cinnamoyl shell of the dendrimers dimerized when irradiated under a UV light by using 5‐nitroacenaphthylene as an initiator in dilute dimethylformamide (DMF). FTIR, ¹H NMR, UV‐Vis, SEC, and a viscosity test certified that the photocycloaddition of the cinnamoyl shell of the dendrimers took place within the molecules with the disappearance of double bond signals in the FTIR. ¹H NMR spectra as well as the intrinsic viscosity and polydispersity value of the products both before and after irradiation showed no difference. It was further found that the cinnamoyl shell‐modified dendrimers possessed fluorescence property, and the fluorescence intensity became stronger when the shell was photocyclized under UV‐ irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4147–4153, 2000     

Fragmentation of poly(amidoamine) dendrimers in matrix-assisted laser desorption

Fragmentation of different generations of poly(amidoamine) dendrimers was explored in five common MALDI matrices: 2,5-dihydroxybenzoic acid (DHB), 4-hydroxy-3-methoxycinnamic acid (FER), α-cyano-4-hydroxycinnamic acid (ACH), 2,4,6-trihydroxyacetophenone (THAP), and 3-hydroxypicolinic acid (HPA). Of these, DHB was the softest matrix and ACH produced significant fragment intensity already at MALDI threshold, FER and THAP being in between. HPA was not a convenient matrix for dendrimers and produced a specific fragmentation pattern. Fragmentation analysis was mainly concentrated on generation G1, which contains already all essential structural elements. Dendrimers showed complicated fragmentation behavior with multiple fragmentation channels in our MALDI experiments. The relative intensities of these channels depended selectively on choice of the matrix and showed dissimilar dependence on the laser pulse energy. This was attributed to different fragmentation mechanisms, due to different protonation pathways, occurring in the same MALDI plume. The fragmentation pathways were proposed for all observed fragmentation channels. All fragmentation sites of protonated ions were found to be directly attached to the protonation sites and the fragmentation was surplus charge driven in this sense. No charge remote fragmentation channels were detected. Cationized dendrimers showed higher stability than the protonated ions.     

Analysis of poly(amidoamine) dendrimer structure by UV-vis spectroscopy

We report a UV-vis spectroscopic study of four different types of poly(amidoamine) dendrimers. The results indicate that the degree of protonation of the interior tertiary amines of these dendrimers correlates directly to an absorption band with λ(max) in the range of 280-285 nm. Specifically, at low pH, the tertiary amines are protonated and the 280-285 nm band is absent. However, at elevated pH, when these groups are deprotonated, this band appears. Similar results were obtained for a simple model compound. The dependence of the 280-285 nm band on the chemical state of the tertiary amines of the dendrimers was confirmed by complexing them with Pd(2+) and Pt(2+). In this case the band disappears, and it only reappears when the metal ions are decomplexed following reduction with BH(4)(-). Finally, filtration experiments showed that the absorption band between 280-285 nm arises exclusively from intact, or nearly intact, dendrimers rather than low-molecular-weight fragments.     

Structural analysis of poly(amidoamine) dendrimer immobilized in crosslinked poly(ethylene glycol)

Polymeric membranes comprised of poly(amidoamine) (PAMAM) dendrimer immobilized in a poly(ethylene glycol) (PEG) network exhibit an excellent CO₂ separation selectivity over H₂. The CO₂ permeability increases with PAMAM dendrimer concentration in the polymeric membrane and becomes 500 times greater than H₂ permeability when the dendrimer content was 50 wt % at ambient conditions (5 kPa of CO₂ partial pressure). However, the detailed morphology of the membrane has not been discussed. The immiscibility of PAMAM dendrimer and PEG matrix results in phase separation, which takes place in a couple of microns scale. Especially, laser scanning confocal microscope captures a 3D morphology of the polymeric blend. The obtained 3D reconstructions demonstrate a bicontinuous structure of PAMAM dendrimer‐rich and PEG‐rich phases, which indicates the presence of PAMAM dendrimer channel penetrating the polymeric membrane, and CO₂ will preferentially pass through the dendrimer channel. In addition, Fourier transform of the 3D reconstructions indicates the presence of a periodic structure. An average size of the dendrimer domain calculated is 2–4 μm in proportion to PAMAM dendrimer concentration. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Preparation and tribological properties of self‐assembled poly(amide amine)‐Cu nanofilm on silicon

Self‐assembled poly(amide amine)‐copper (PAMAM/Cu) film on silicon was prepared and investigated by means of contact angle measurement, XPS and atomic force microscopy (AFM). The tribological properties were evaluated using a reciprocal ball‐on‐disc test rig and a lateral force microscope. Results of XPS show the existence of Cu(0) and PAMAM molecule on the surface of the film. Compared with the self‐assembled monolayer of the poly(amide amine) generation 4.0 dendrimer, the friction force of PAMAM/Cu film is lower and the friction coefficient is smaller which can be attributed to the existence of Cu nanoparticles. The PAMAM/Cu film shows a good lubrication effect. The stability of friction and wear resistance of film is improved. Copyright © 2011 John Wiley & Sons, Ltd.     

Photodegradation of poly(amidoamine) dendrimers peripherally modified with 1,8-naphthalimide units

This paper presents the photophysical and photochemical characteristics of four new poly(amidoamine) dendrimers of zero and second generation whose periphery has been modified with 1,8-naphthalimide units. Nitro- and allylamino groups have been used as substitutents at the C-4 position of the 1,8-naphthalimide fluorophores. The discussion is focused on the photodegradation of the dendrimers in N,N-dimethylformamide and dioxan solutions. Investigations have shown that the photodegradation of the dendrimers with 4-nitro substituted 1,8-naphthalimide proceed with yellow colour development in the solvent while no colour changes followed the same process in dendrimers with allylamino group substituent. The results also show that the photostability of the dendrimers depends on their generation.     

Study on interaction between poly(amidoamine) dendrimer and CdSe nanocrystal in chloroform

The binding of different categories of molecules to quantum dot has been studied for many years through different spectroscopic techniques to elucidate details of binding mechanism. In this work we present the results of the study of the interactions between CdSe and poly(amidoamine) dendrimer monitored by photoluminescence spectroscopy of CdSe in chloroform. Dendrimers with different terminal groups and different generations were used to bind with CdSe nanocrystal of different size. Significant differences in the values of binding constant Kb(n) and K(SV) were found in these experiments. The binding constant for poly(amidoamine) dendrimer of generation 4.0 is higher as compared to generation 3.5. The interaction of CdSe with poly(amidoamine) dendrimer shows an increase of binding constants with increasing dendrimer generation from 2.0 to 4.0, as well as with decreasing CdSe diameter. From HRTEM and FTIR analysis, we suggest that dendrimer/CdSe interactions are primarily hydrogen-bonding.     

聚酰胺-胺的酸碱电位滴定分析

聚酰胺-胺(PAMAM)是一种有着广泛用途的树形大分子,酸碱滴定分析可以表征合成的PAMAM中所含的伯胺基及叔胺基的数量,因此作为一种重要的辅助表征手段被PAMAM的合成及改性研究者所采用。文章对该方法原理进行了详细的论述,说明了滴定过程中产生的酰胺键水解不影响滴定及计算结果。通过实验表明在pH<2的条件下滴定可以保证叔胺的充分质子化。     

Synthesis of on resin poly(propylene imine) dendrimer and its use as organocatalyst

Solid phase synthesis of poly(propylene imine) dendrimer is described. An iterative synthesis including double Michael addition of acrylonitrile to the primary amino groups on crosslinked polystyrene support followed by reduction of nitrile groups to amino groups give poly(propylene imine) dendrimers up to third generation attached to the polystyrene support. The supported dendrimer is used as an organocatalyst to Knoevenagel condensations. The supported catalyst showed good selectivity and the product was obtained in excellent yield under green reaction conditions. Densely packed amino groups enhance catalysis by a co-operative effect. The catalyst is recoverable and reusable.     

SiO2–poly(amidoamine) dendrimer inorganic/organic hybrids

SiO₂–poly(amidoamine) (PAMAM) dendrimer hybrids were synthesized via (1) a Michael addition reaction between the dendrimer and 3‐(trimethoxysilyl) propyl acrylate, (2) the dissolution of the formed compound in methanol, and (3) the mixing of the latter solution with a methanol solution of partly hydrolyzed tetraethylorthosilicate (TEOS) and its casting on a glass substrate. ¹H NMR indicated that in the first step, 77% of the secondary amines were converted into tertiary amines when the fourth‐generation dendrimer was employed and 46% were converted when the second‐generation dendrimer was used. The final SiO₂–PAMAM dendrimer hybrids were obtained via the hydrolysis and condensation of the compound obtained via the Michael addition and the methanol solution of partly hydrolyzed TEOS. The compartmentalized structure of the hybrids due to the compartments of the dendrimers could be controlled by changing the dendrimer and the amount of TEOS. Scanning electron microscopy and transmission electron microscopy micrographs provided information about the structure of the hybrids. Like the PAMAM dendrimer, the SiO₂–PAMAM dendrimer hybrids exhibited a high metal ion complexing capacity because of the presence of the compartments of the dendrimer; they can be, however, much more easily handled, and, as demonstrated by thermogravimetric experiments, have much higher thermal resistance. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1443–1449, 2000     

以枝形大分子聚酰胺-胺(PAMAM)为键合固定相的开管毛细管电色谱柱的制备及评价

用3-氨丙基三乙氧基硅烷(KH550)作偶联剂, 在毛细管内壁上逐步合成树枝形大分子聚酰胺-胺(PAMAM), 制得了1, 2和3代PAMAM键合的开管毛细管电色谱柱, 并对其性能进行了研究. 结果表明, 随着大分子代数的增加, 毛细管电渗流(EOF)逐步下降. 利用制得的1, 2和3代PAMAM修饰的开管毛细管电色谱柱对丙氨酸和脯氨酸的分离进行对比, 结果显示, 随着大分子PAMAM代数的增加, 分离度逐步增大, 丙氨酸和脯氨酸可在3代树枝状大分子PAMAM修饰的开管毛细管电色谱柱上达到基线分离. 采用非衍生化法和3代PAMAM修饰的开管毛细管电色谱柱成功地分析了精氨酸、 丙氨酸、 脯氨酸、 甲硫氨酸和组氨酸. 结果表明, 键合毛细管柱具有良好的重现性和稳定性.     

Visual observation of avidin-biotin affinity by fluorescent G4.5 poly(amidoamine) dendrimer

An air-treated G4.5 poly(amidoamine) (PAMAM) dendrimer displayed the enhanced fluorescence enough to be utilized as a fluorescence marker to visualize avidin-biotin affinity: On a fluorescence microscopic image, the avidin labeled by a fluorescent G4.5 PAMAM dendrimer was observed to be selectively bound on the biotin pattern that was prepared by amide-bonding of biotin on a carboxylic acid-terminated self-assembled monolayer and in turn by UV-irradiation with a photomask on the monolayer.     

A novel fluorescent sensor for Cr3+ based on rhodamine-cored poly (amidoamine) dendrimer

A novel poly (amidoamine) (PAMAM) dendrimer, comprising rhodamine B unit in the core and 1-phenyl-3-methyl-5-pyrazolone unit at the periphery, has been synthesized and characterized. The dendrimer shows dramatic increase in its fluorescence intensity in the presence of proton and metal cations, especially in the presence of Cr(3+). The complex formed by dendrimer and Cr(3+) in ethanol solution has also been studied, considering the potential application for Cr(3+) fluorescent sensor. The influence of the unique chemical structure and resulted photoinduced electron transfer, as well as spirolactam ring-opening on the photophysical properties of the product has been investigated.